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Data Interpretation: Methods and Tools

Just how Predictable is Predictive Lighting?

by Kate Devlin

ABSTRACT
Predictive lighting refers to the use of computer modelling software to accurately simulate the behaviour of light, resulting in a virtual scene that physically represents the real world in terms of illumination, providing images that appear – and aim to be – ‘realistic’. Predictive lighting has been used in areas such as architectural simulations and forensic reconstructions, and also in the representation of archaeological sites and artefacts, with the aim of depicting the environment as it would have looked to an observer situated within it. This method uses information about the geometry of an environment, the material properties of the surfaces in that environment and the spectral properties of the light sources to generate a mathematical simulation that we can, to some degree, consider accurate. This enables us to explore new hypotheses and examine the way in which things were viewed and understood in the past by manipulating variables and working with virtual objects in a way that is not possible with a real site or artefact.

However, leaving aside the contentious issues of the representation content itself, the use of predictive lighting has its own limitations. While we can simulate lighting values and their distribution in a scene, we cannot yet say with complete confidence that we have achieved a perceptual match between what people see when they look at our computer model and what they would see in a real-world equivalent. This is due to factors such as display restrictions and aspects of the human visual system such as colour and brightness perception, which affect our interpretation of the output images. Such issues can also influence any images displayed in an electronic manner, as control of the visual output is often reduced or lost after the rendering process is complete. In order to state authoritatively that our images are valid, it is necessary to determine the degree of certainty that we have in the process, and make this evaluation transparent to the user.

This paper discusses how predictive lighting may be used to present a visual interpretation of the past, and how problematic areas might be addressed in order to achieve a more objective visualization of the illumination of past environments.